/Engine/Source/Runtime/CoreUObject/Public/UObject/UObjectGlobals.h
Delegate type for reachability analysis external roots callback. First parameter isFGarbageCollectionTracerto use for tracing, second is flags with which objects should be kept alive regardless, third is whether to force single threading
typedef TMulticastDelegate_ThreeParams< void, [FGarbageCollectionTracer](API\Runtime\CoreUObject\UObject\FGarbageCollectionTracer) &, EObjectFlags, bool > FTraceExternalRootsForReachabilityAnalysisDelegate